This work presents a study of welded gap K- and KT-joints formed by seamless steel hollow structural sections with rectangular hollow section for the chords and circular hollow section for the members. The study involves the generation, analysis and calibration of numerical models based on the finite element method, by comparison with experimental results previously obtained with full-scale prototypes. Several models were analyzed with shell elements, evaluating the radius of corner influence on the rectangular hollow section, as well as some modeling alternatives of the welds in the connections. The results of the computational analysis are in good agreement with the experimental results.